Since GM does not list there advertised duration of their cams, does anyone have a idea what the zz4 cam has for advertised duration?

I have been led to believe that it is 275/280 on a 112/109 lsa.

I'm not sure this is correct, seems kind of big to me.

I was thinking it was more in line with something like 256/265.

 

That would depend on how it was measured...

GM measures their cams at .001" of lobe lift or some such. As a result, all of their cams look HUGE, but of course they're really not.

Crane measures theirs at .004". Comp and most others measure theirs at .006" which makes them impossible to directly compare (the Cranes always "appear" to have lazy ramps).

275/280 sounds about right for GM's methodology; a little on the low side, if anything.

 

So if you measured it by Comps method, what would the advertised duration be of the zz4 cam?

 

I'd guess probably something like 250/258. Just as a guess.

 

Maybe someone put one on a cam doctor. Then we would know for sure.

 

Kind of figure something like that.

 

Well, I think it may be bigger than that. I ran it through a DCR calculator with that specs on the cam it has a 8.5 DCR. I ran it with a 255/265 and it was like 8.4. So, I would say no larger than 260.

Higher than 8.4 on a DCR and it would have to run race fuel.

 

http://www.gmgoodwrench.com/GMPerfor...talog_2006.pdf


its on page 34.

 

No advertised duration is listed. Only @ .050.

 

here is a zz4 cam spec card another member (sorry can't remember who) posted a while back. At .006 it is 264/273

 

Thanks for the posting of the ZZ4 cam specs. It is interesting to see how it compares to the XFI 268 cam. Seat to seat there is not that much of a difference. At .050" there is a larger difference. AT .200 lift there is even a greater difference.
Comparing the new versus the old. Me, I went with the XFI 268.

At .006 lift.
ZZ4: 264/273
XFI 268: 268/274

At .050 lift.
ZZ4: 208/221
XFI 268: 218/224

At .200 lift:
ZZ4: 125/142
XFI 268: 143/147

 

The xfi 268 has a faster flank speed over the zz4, getting those valves opening and closing faster making more horsepower, interesting comparison.

 

Yes, it really shows the difference in the acceleration rate of the lobes. I bet the idle and vacuum is not that much different either because of the similiarity of the valve durations at .006". Horsepower and rpm wise there is a big difference. The cylinders are filling at a much faster rate with the 268XFI cam.

 

I have a 280XFI in my 312. 423 FWHP out of a moded 305 with TBI on top of it.

 

Yep, that's what aggressive ramps will do for you. CompCams has a series of lobes they name CRC (Constant Radius of Curvature) which are an excellent example of this.

On one, you can get .576 valve lift using only a 1.5 rocker yet duration is only 224 @ .050; install a 1.6 and you'd have a tad over .600

Jake

 

Who is making this 280 XFI and the 268 XFI?

 

Competition Cams.

 

Yep!

And if you want a camshaft that's designed and ground with cutting edge technology, CompCams is the company - 2nd to NONE!.

He** even Harvey CRANE said they're at the top of the hill, and for CRANE to admit to that, it's got to carry enormous weight.

Jake

 

The Comp XFI cams lift ratings ARE WITH 1.6:1 rockers!!!!! They even tell you that they are designed to run with 1.6:1 rockers.